Some control technologies to promote activation of an exhaust gas cleaning catalyst during an engine warming up process have been proposed for an engine comprising an injector and a spark plug provided in a combustion chamber. For example, JP 2006-052687 A discloses a control device for an internal combustion engine. The internal combustion engine comprises an injector, a spark plug and an exhaust gas cleaning catalyst. The injector is provided substantially at a center of an upper part of a combustion chamber and is configured to inject fuel into a cylinder directly. The;spark plug is provided at a portion in the upper part of the combustion chamber where a part of fuel spray from the injector reaches directly. The exhaust gas cleaning catalyst is provided in an exhaust passage. The control device is configured to perform an injection by the injector and an ignition by the spark plug in an expansion stroke to promote the activation of the exhaust gas cleaning catalyst.
The injection and the ignition in the expansion stroke are additionally performed after an injection and a subsequent ignition are performed in an intake stroke or a compression stroke. Specifically, a first time injection and a subsequent first time ignition are performed in the intake stroke or the compression stroke. Then, a second time injection and a subsequent second time ignition are performed in the middle to latter period of the expansion stroke to activate the exhaust gas cleaning catalyst. The second time fuel injection amount is set to be smaller than the first time fuel injection amount, and the second time ignition is performed before the fuel spray injected by the second time injection reaches a wall surface of the combustion chamber. Since a positional relationship between the injector and the spark plug is as described above and the second time ignition is performed at the timing described above, this control device allows almost all of fuel injected by the second time injection to be burned, thereby increasing the exhaust gas temperature.
The present inventors are considering a control for activating an exhaust gas cleaning catalyst in an engine configuration different from that disclosed in JP 2006-052687 A. The engine configuration under consideration is common to the engine configuration in the same publication in that both of an injector and a spark plug are provided in an upper part of a combustion chamber, and a part of fuel spray from the injector proceeds toward the spark plug. However, the engine configuration under consideration is different from the engine configuration in the same publication in that an electrode part of the spark plug is disposed in an area above a contour surface of a fuel spray pattern which is closest to the spark plug. Furthermore, the engine configuration under consideration is different from the engine configuration in the same publication in that a tumble flow is formed from intake air supplied into the combustion chamber, and the spark plug is disposed on a downstream side of the injector when viewing in a tumble flow direction.
The tumble flow formed in the combustion chamber swirls from the upper part of the combustion chamber downward at an exhaust port side and from a lower part of the combustion chamber upward at an intake port side. The control is being considered assuming such a tumble flow. Specifically, the control under consideration is performed so that first time injection is performed in an intake stroke to allow the fuel spray to swirl together with the tumble flow in the combustion chamber, and a timing of ignition by the spark plug is set to a timing retarded from a compression top dead center. In addition, in the control under consideration, a discharge period at the aforementioned electrode portion is set on a retard side of compression top dead center, and injection is also performed in this discharge period. The fuel injected from the injector in a high pressure state forms a low pressure area by entraining air around the fuel (entrainment). Therefore, when injection is performed during the discharge period, a discharge spark that arises at the electrode portion is attracted by the low pressure area that is formed around the fuel spray in the direction of the spark plug
When a second ignition is performed after a second injection that is performed from a middle period to a latter period of an expansion stroke such as described in JP 2006-052687 A in a combustion chamber in which a tumble flow is occurring, during a period until the second ignition is started, the shape of a fuel spray produced by the second injection is liable to change due to the influence of the tumble flow or the in-cylinder pressure. Therefore, unless the positional design of the injector is performed taking into consideration the smoldering around the plug of the spark plug, or an optimal injection timing of the injector is selected, the concentration of an air-fuel mixture surrounding the spark plug will be unstable and combustion fluctuations will be large. In this respect, by utilizing the above described attraction action, a fuel spray that is produced by an injection during a discharge period caused by a discharge spark that is attracted by the aforementioned low pressure area can be combusted, and thus an initial flame which, at approximately the same timing as the fuel spray and discharge spark, arises from the discharge spark and the air-fuel mixture that includes a fuel spray produced by injection in the intake stroke that occur can be caused to grow to a certain extent. Therefore, combustion of a fuel spray produced by injection in the expansion stroke can be stabilized, and combustion fluctuations can be suppressed.
However, in the above described attraction action, a distance between a contour surface of the fuel spray in the direction of the spark plug that is produced by injection during the discharge period and the electrode portion is important. Therefore, when this distance increases, there is a possibility that the attraction action will be insufficient. Even when the attraction action is insufficient, it is possible to cause an initial flame to grow from an air-fuel mixture including a fuel spray produced by injection during the discharge period. However, the fact that the attraction action is insufficient means that the discharge spark is not sufficiently drawn to the fuel spray produced by an injection during the discharge period, and the concentration of the air-fuel mixture around the discharge spark is not high. Hence, when the attraction action is insufficient, growth of an initial flame is inhibited. Further, with respect to combustion cycles during the control under consideration, if there are many cycles in which such a situation occurs, combustion fluctuations between cycles will be large, and therefore drivability will be affected.
The present disclosure addresses the above described problem, and an object of the present disclosure is, in a case of performing activation control of an exhaust gas purification catalyst by means of an engine configuration in which some fuel spray from an injector travels in a direction of a spark plug that is disposed on a downstream side in a flow direction of a tumble flow, and an electrode portion of the spark plug is disposed in an area that is above a contour surface of the fuel spray that comes closest to the spark plug, to provide a countermeasure for a time when a distance between the contour surface and the electrode portion increases.
A control device for an internal combustion engine according to the present disclosure is a control device for controlling an internal combustion engine that includes: an injector which is provided in an upper portion of a combustion chamber and which directly injects fuel into a cylinder; a spark plug which ignites an air-fuel mixture inside a cylinder using a discharge spark that is generated at an electrode portion, and which is provided at a position that is at the upper portion of the combustion chamber and is on a downstream side relative to the injector in a flow direction of a tumble flow that is formed inside the combustion chamber, and is provided so that a position of the electrode portion is above a contour surface of a fuel spray that is injected toward the spark plug from the injector; and an exhaust gas purification catalyst that purifies exhaust gas from the combustion chamber. The control device is configured to control at least fuel injection by the injector and a discharge at the electrode portion by the spark plug. The control device is further configured to control the injector so as to perform an intake stroke injection and an expansion stroke injection that activate the exhaust gas purification catalyst and control the spark plug so as to generate a discharge spark at the electrode portion over a predetermined period that is a predetermined period on a retard side of compression top dead center and that includes a period in which the expansion stroke injection is performed. The control device is further configured to, when it is determined that a growth rate of an initial flame which arises from a discharge spark and which grows while engulfing a fuel spray produced by the expansion stroke injection in the predetermined period is less than a first determination value, control the injector so as to perform, in addition to the intake stroke injection and the expansion stroke injection, an additional injection at a timing that is on a retard side relative to compression top dead center and is on an advance side relative to an occurrence timing of the discharge spark at the electrode portion.
Since a fuel spray that is produced by the additional injection is carried in a downstream direction by the tumble flow, the fuel spray moves as far as the vicinity of the electrode portion at the time the expansion stroke injection is performed. Further, since a discharge spark occurs at the electrode portion at the time that the expansion stroke injection is performed, an initial flame that is produced based on an air-fuel mixture including a fuel spray produced by an injection and a discharge spark in the intake stroke grows at once as a result of engulfing the fuel spray produced by the additional injection. That is, by performing the additional injection, a time period until the initial flame engulfs the fuel spray produced by the expansion stroke injection is shortened.
The control device for an internal combustion engine according to the present disclosure may control the injector so that an injection amount of the additional injection is less than an injection amount of the expansion stroke injection.
Because the injection timing of the additional injection is on the retard side of compression top dead center, and is on an advance side relative to the predetermined period, if the injection amount of the additional injection is large, fuel is liable to adhere to a top face of a descending piston. In this respect, by making the injection amount of the additional injection less than the injection amount of the expansion stroke injection, occurrence of the aforementioned adherence of fuel is suppressed and an increase in a particulate number that is one object of emissions regulations is suppressed.
When it is determined that the growth rate is less than the first determination value, the control device for an internal combustion engine according to the present disclosure may control the injector so as to progressively increase an injection amount of the additional injection as a difference between the growth rate and the first determination value increases.
As described above, by performing the additional injection, a time period until the initial flame engulfs the fuel spray that is produced by the expansion stroke injection is shortened. However, when it is determined that the growth rate of the initial flame is significantly lower than the first determination value, even if an additional injection is performed thereafter, there is a possibility that a time period until the initial flame engulfs the fuel spray that is produced by the expansion stroke injection will not be shortened sufficiently. In this respect, by progressively increasing the injection amount of the additional injection as a difference between the growth rate of the initial flame and the first determination value increases, it is possible to sufficiently shorten the time period until the initial flame engulfs the fuel spray that is produced by the expansion stroke injection.
When it is determined that the growth rate is still lower than the first determination value even though the injector is controlled so as to perform the additional injection, the control device for an internal combustion engine according to the present disclosure may control the injector so as to increase an injection amount of the expansion stroke injection, or control the injector so as to advance an injection timing of the expansion stroke injection and control the spark plug so as to advance the occurrence timing.
If the injection amount of the expansion stroke injection is increased, a fuel spray produced by the expansion stroke injection will disperse over a wider area, and hence a time period until the initial flame that grows by engulfing the fuel spray produced by the additional injection engulfs the fuel spray produced by the expansion stroke injection will be shortened.
If the injection timing of the expansion stroke injection and the start timing of the predetermined period are advanced, the in-cylinder pressure rises. When the in-cylinder pressure is high, it becomes difficult for the fuel spray produced by the expansion stroke injection to disperse in the travelling direction, and therefore the fuel spray becomes thick. If the fuel spray produced by the expansion stroke injection becomes thick, a distance between a contour surface of the fuel spray that proceeds in the direction of the spark plug and the electrode portion is shortened, and therefore the time period until the initial flame that grows by engulfing the fuel spray produced by the additional injection engulfs the fuel spray produced by the expansion stroke injection will be shortened.
When it is determined that, as a result of controlling the injector so as to perform the additional injection, the growth rate exceeds a second determination value that is greater than the first determination value, the control device for an internal combustion engine according to the present disclosure may control the injector so as to decrease an injection amount of the expansion stroke injection, or control the injector so as to retard an injection timing of the expansion stroke injection, or control the spark plug so as to advance a start timing of the predetermined period, or control the injector so as to retard an injection timing of the expansion stroke injection and control the spark plug so as to retard the occurrence timing.
If the injection amount of the expansion stroke injection is decreased, a fuel spray produced by the expansion stroke injection will disperse in a narrower range, and therefore a time period until an initial flame that grows by engulfing a fuel spray produced by the additional injection further engulfs a fuel spray produced by the gbexpansion stroke injection will lengthen.
If the injection timing of the expansion stroke injection is retarded, a time period until an initial flame that grows by engulfing a fuel spray produced by the additional injection further engulfs a fuel spray produced by the expansion stroke injection will lengthen.
If the occurrence timing of a discharge spark at the electrode portion is advanced, although an initial flame that arises from the discharge spark will engulf a fuel spray produced by the additional injection and grow in an early stage, a time period until the initial flame further engulfs a fuel spray produced by the expansion stroke injection will lengthen.
If the injection timing of the expansion stroke injection and the occurrence timing of a discharge spark at the electrode portion are retarded, the in-cylinder pressure will decrease. If the in-cylinder pressure decreases, it becomes easy for a fuel spray that is produced by the expansion stroke injection to disperse in the travelling direction, and therefore the fuel spray becomes narrower. If the fuel spray produced by the expansion stroke injection becomes narrower, a distance between the electrode portion and the contour surface of the fuel spray travelling in the direction of the spark plug will increase, and therefore a time period until an initial flame that grows by engulfing a fuel spray produced by the additional injection further engulfs a fuel spray produced by the expansion stroke injection will lengthen.
The control device for an internal combustion engine according to the present disclosure may perform a determination with respect to the growth rate based on a crank angle period until a mass fraction burned becomes 10% from 0% after occurrence of a discharge spark at the electrode portion.
It is possible to make a determination regarding the growth rate of an initial flame if the determination is based on a crank angle period until a mass fraction burned becomes 10% from 0% after the occurrence of a discharge spark at the electrode portion.
According to the control device for an internal combustion engine of the present disclosure, when a distance between an electrode portion and a contour surface of a fuel spray which travels in the direction of a spark plug and which is produced by an injection during a discharge period increases, it is possible for a time period until an initial flame that grows by engulfing a fuel spray produced by an additional injection further engulfs a fuel spray produced by an expansion stroke injection to be confined within an optimal range. Hence, combustion fluctuations between cycles can be made small and the influence of such combustion fluctuations on drivability can be favorably suppressed.